<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        //++ -- + -
        var num = 3;
        var a = ++num;

        document.write(a + "<br>")
        document.write(num + "<br>")


        // + 装换问题

        var str = +"123";
        document.write(str + "<br>");
        document.write(typeof (str));


        var str1 = +"abc";
        document.write(str1 + "_____" + typeof (str1) + "<br>");

        var flag = +true;
        var flag1 = +false;

        document.write(flag + "_____" + typeof (flag) + "<br>");
        document.write(flag1 + "_____" + typeof (flag1) + "<br>");


    </script>
</head>
<body>

</body>
</html>